feat(studio): trust pass — friendly errors + store clarity + MCP i18n

Second half of the May-2026 trust pass. Drops the wall of
gRPC trailers from every error surface and makes the Store
honest about what is and isn't installable.

Friendly errors:

- New `friendlyError(Object, AppLocalizations)` mapper turns
  GrpcError + arbitrary throwables into a localised headline,
  optional recovery hint, and a verbatim detail string kept
  behind a "Show details" expander. Duck-typed on `.code` /
  `.message` so Studio doesn't have to depend on package:grpc
  directly.
- `FaiErrorBox` gains an `error:` constructor that runs the
  mapper. Every call site that used to render
  `snap.error.toString()` (flows, welcome, store) switches to
  it.
- 9 .arb entries per locale cover the gRPC codes we actually
  emit (INVALID_ARGUMENT, NOT_FOUND, ALREADY_EXISTS,
  PERMISSION_DENIED, FAILED_PRECONDITION, INTERNAL,
  UNAVAILABLE, UNAUTHENTICATED) plus copy/details affordances.
- `test/friendly_error_test.dart` — 6 unit tests for the
  mapper. Covers the mapping table, locale-switching, and the
  non-gRPC fallback so future regressions show up in CI.

Capability discovery:

- New `HubService.allCapabilities()` reads the kind-aware
  capability list (wasm + builtin + federated) and returns a
  Dart-side `CapabilityInfo` value type. The flow page's
  missing-dependency check uses it so `system.approval` and
  federated MCP/n8n tools count as "available" — fixes the
  Run button staying disabled forever.
- `HubService.listModules()` filters to kind=wasm so the
  Modules page doesn't sprout synthetic "system" entries that
  the operator can't uninstall.

Store clarity:

- New "Installable only" filter, on by default. Roughly 2/3
  of seed entries currently carry `status: planned`; the
  default view stops being noise.
- Featured-strip cards for planned modules now show a
  "Coming soon" pill instead of an empty action area.
- Main-grid cards for non-installable modules dim to 60%
  opacity so the eye lands on actionable cards first.
- Detail-sheet "Nicht installierbar" tooltip → inline hint
  box. The reason is visible without hovering.

MCP localisation:

- `_kMcpSuggestions` no longer holds 11 hardcoded English
  description strings. The `description` field is replaced
  with a `resolveDescription(AppLocalizations)` lookup that
  switches on the suggestion `name` to read the matching
  `mcpSuggestion*Desc` .arb key. EN + DE shipped.
- New `FaiEnBadge` widget renders a small `[EN]` pill when
  the active locale isn't English. Used next to MCP /
  federated store entries' tagline + description because
  the server supplies them in English and we can't translate
  on the fly yet — the badge is the honest signal until the
  planned `studio.translate` plugin lands.

Plus housekeeping: removed the unused `_keepImport` lint
escape in the test and the dangling library doc-comment in
`format.dart`.

Signed-off-by: flemming-it <sf@flemming.it>
Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_en.arb

@@ -76,6 +76,25 @@
   "buttonReadDocs": "Read docs",
   "buttonCopy": "Copy to clipboard",
   "buttonCopied": "Copied",
+  "buttonShowDetails": "Show details",
+  "buttonHideDetails": "Hide details",
+  "storeInstallableOnly": "Installable only",
+  "storePillComingSoon": "Coming soon",
+  "storeNotInstallableInline": "This module is on the roadmap (status: {status}). It has no installable bundle yet — follow the repository for updates.",
+  "@storeNotInstallableInline": { "placeholders": { "status": { "type": "String" } } },
+
+  "mcpSuggestionDeepwikiDesc": "Public HTTPS — GitHub repo documentation search (AI-powered). No Node, no API key.",
+  "mcpSuggestionSemgrepDesc": "Public HTTPS — security scanning for code vulnerabilities. No Node, no API key.",
+  "mcpSuggestionFilesystemDesc": "Anthropic — read / write files in /tmp. Edit the path before saving.",
+  "mcpSuggestionFetchDesc": "Anthropic — fetch arbitrary HTTP(S) URLs as markdown.",
+  "mcpSuggestionGithubDesc": "Anthropic — issues, PRs, repo files. Needs a GitHub PAT in the env var.",
+  "mcpSuggestionPuppeteerDesc": "Anthropic — headless browser automation for screenshots / scraping.",
+  "mcpSuggestionPostgresDesc": "Anthropic — read-only SQL queries against a Postgres database. Edit the URL.",
+  "mcpSuggestionSqliteDesc": "Anthropic — query a local SQLite file. Edit the path.",
+  "mcpSuggestionBraveSearchDesc": "Anthropic — web search via Brave. API key required.",
+  "mcpSuggestionMemoryDesc": "Anthropic — persistent knowledge graph for an agent's memory.",
+  "mcpSuggestionTimeDesc": "Anthropic — current time + timezone conversion.",
+  "mcpServerEnLanguageBadge": "Server text in English — Studio shows it as supplied.",
 
   "settingsTitle": "Hub endpoint",
   "settingsHost": "Host",
@@ -513,6 +532,25 @@
   "@flowsErrorTitle": { "placeholders": { "name": { "type": "String" } } },
   "flowsRunning": "Flow running…",
   "flowsNoOutputs": "Flow completed with no declared outputs.",
+
+  "errGeneric": "Something went wrong.",
+  "errInvalidArgument": "Invalid input.",
+  "errInvalidArgumentHint": "Check the form values and try again.",
+  "errNotFound": "Not found.",
+  "errNotFoundHint": "The item you asked for isn't here — it may have been removed or never existed.",
+  "errAlreadyExists": "Already exists.",
+  "errPermissionDenied": "Permission denied.",
+  "errPermissionDeniedHint": "The hub's operator policy blocks this action. Check `~/.fai/config.yaml`.",
+  "errFailedPrecondition": "Setup issue blocked this.",
+  "errFailedPreconditionHint": "The hub couldn't proceed because something it needs isn't ready. The detail below explains what.",
+  "errInternal": "Unexpected internal error.",
+  "errInternalHint": "Check the hub logs at `~/.fai/logs/`. If this repeats, please report it.",
+  "errUnavailable": "Hub not reachable.",
+  "errUnavailableHint": "Make sure `fai serve` (or `fai daemon start`) is running and the daemon endpoint matches Studio's settings.",
+  "errUnauthenticated": "Authentication required.",
+  "errUnauthenticatedHint": "Set `FAI_REGISTRY_TOKEN` or sign in through Settings before retrying.",
+  "errCopyDetail": "Copy detail",
+  "errDetailCopied": "Detail copied to clipboard.",
   "flowsOutputUnknown": "Output payload variant not recognised.",
   "flowsOutputBytesUnknownMime": "binary",
   "flowsOutputSaveAs": "Save as…",